Obtaining accurate flow measurements from a small nominal diameter oval gear flowmeter is important if such instruments are to be used in industry. In oval gear flowmeters, the oval gears permit a known volume of fluid to flow through a fluid path in a measuring chamber for determining the volume or rate of the flowing fluid. As fluid flows through the measuring chamber, the oval gears rotate due to the minimal differential pressure created in the measuring chamber. The rotation of the oval gears form movable separation walls that prevent a direct through flow of fluid through the measuring chamber. The oval gears however, allow the through flow of a known quantity of fluid to pass through the measuring chamber as said oval gears rotate. The oval gears are engaged to shafts which contact various display devices for enumerating the flow rate.
Precision of the flowmeter is strongly dependent on minimizing seepage at the seal surfaces. Seal surfaces involved include surfaces of the gears and housing in both the radial and axial directions. Tight seals must be maintained between the gear and the housing to prevent flow from bypassing the measuring chamber. This is particularly true for small sized flowmeters which have small diameter oval gears, i.e. smaller than 20 mm. Obviously, for smaller sized flowmeters, seepage can account for a greater percentage of the total flow in comparison to large devices. However, tighter seals involving closer machined tolerances and smaller gaps can increase friction, produce excessive differential pressure across the flowmeter and misalignment in the chamber. This can result in jamming and oval gear rotation difficulties.
A primary problem in obtaining accurate flow measurements from oval gear flowmeters is minimizing the axial gaps and the radial gaps between the oval gears and the measuring chamber walls. Another problem in obtaining accurate flow measurements from oval gear flowmeters is minimizing the differential pressure in the measuring chamber. Oval gear flowmeters with small nominal diameters require a high manufacturing-technical standard to guarantee small gaps and easy rotation of the oval gears. Oval gears of small nominal diameters, i.e., smaller than 20 mm, have a much greater effect on the flow measurement accuracy as compared to oval gears of larger nominal diameters. When the gaps between the frontal surfaces of the oval gears and the opposite axial measuring chamber walls are made smaller, even slight misalignments between the oval gears and the axial measuring chamber walls will be noticed. Misalignment that leads to a deviation in the parallel arrangement between the frontal surfaces of the oval gears and the corresponding axial measuring chamber walls, may result in a contact between the oval gears and the measuring chamber wall, causing an interruption in the rotation of the oval gears.
Many problems are associated with prior known oval gear flowmeters. Difficulties arise when the oval gears are rigidly supported in housings on fixed spindles which are not self aligning. Contact between the oval gears and the measuring chamber walls is an existing problem. Another common problem of the prior known oval gear flowmeters is the tendency for the axial position, as well as the angular position of the oval gears to change easily.
There is, therefore, a need for an oval gear flowmeter that avoids the problems of the prior known flowmeters.
A feature of the present invention is to provide an oval gear flowmeter where the oval gear frontal surfaces are parallel and align themselves automatically on the parallel inside surfaces of the measuring chamber.
Another feature of the present invention is to provide an oval gear flowmeter where the oval gears are connected to a shaft by a locking pin placed traversely through an opening in the shaft, wherein the opening in the shaft is aligned with a groove in the top surface of the oval gears.
Yet another feature of the present invention is to provide an oval gear flowmeter where the oval gears are supported in the measuring chamber such that alignment errors in the shaft support may be equalized without increasing the axial gap.
Yet still another feature of the present invention is to provide an oval gear flowmeter for small nominal diameters that has small gaps between the gears and the measuring chamber wall.
Another feature of the present invention is to provide an oval gear flowmeter where the oval gears turn without restriction when engaged with fluid.
Still another feature of the present invention is to provide an oval gear flowmeter that prevents restrictive contact between the oval gear and the measuring chamber wall by means of an automatic aligning of the oval gears.